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He's been charged with product tampering and fraudulently obtaining drugs

A federal grand jury in New Hampshire has indicted a former hospital worker on fraud and product-tampering charges in connection with an outbreak of hepatitis C that sickened more than 30 people, prosecutors announced Thursday.

Investigators say 33-year-old David Kwiatkowski injected himself with syringes of fentanyl, a powerful painkiller, that he stole from patients who were scheduled for surgery. He began working at New Hampshire's Exeter Hospital in April 2011, 10 months after being diagnosed with hepatitis C, a sometimes-fatal virus that attacks the liver.

"Kwiatkowski used the stolen syringes to inject himself, causing them to become tainted with his infected blood, before filling them with saline and then replacing them for use in the medical procedure," the U.S. attorney's office in Concord, New Hampshire, said in a statement announcing the charges. "Consequently, instead of receiving the prescribed dose of fentanyl, patients instead received saline tainted by Kwiatkowski's infected blood."

Kwiatkowski has been charged with seven counts of tampering with a consumer product and seven counts of obtaining controlled substances by fraud, prosecutors said. He was arrested in July and had previously worked as a traveling medical technician on a contract basis for hospitals in Arizona, Georgia, Kansas, Maryland, Michigan, New York and Pennsylvania, officials in those states confirmed.

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He was fired from an Arizona hospital in 2010 after a fellow employee found him passed out in the men's room with a syringe floating in the toilet, according to documents obtained by CNN. A spokeswoman for the Arizona Heart Hospital said Kwiatkowski was immediately fired, and he relinquished his license as a radiologic technologist.

The agency that placed him in the Arizona job, Springboard, Inc., reported the incident to the American Registry of Radiologic Technologists, according to a spokeswoman for the agency. But the association didn't punish Kwiatkowski, telling CNN in July that Kwiatkowski had passed a drug screen the following day, and there was no indication at that time that he had been infected with the hepatitis virus.

The group said police had investigated the case but did not file any criminal charges, and a state agency that regulates radiological medicine said its investigation ended when Kwiatkowski left Arizona.